Add pgo build type

Add pgo build type

One of the ways we can optimize our builds is with profile guided
optimization.  This entails doing several things:

1) Building with --coverage
2) Running an application against the openssl library from step (1) to
   generate profile data
3) rebuilding openssl using the input profile from step (2) to optimize
   the build.

This new build configuration will let developers use the profiled data
to see what type of optimizations might be possible, as well as giving
end users the ability to squeeze a bit more performance out of openssl

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <ppzgs1@gmail.com>
(Merged from https://github.com/openssl/openssl/pull/27839)